When a user wants to transfer display data of a personal computer to project it by a projector, the user firstly mounts a medium on the projector to depress a dedicated button of a remote controller. Then, since a variety of items of information including random numbers generated from the projector are stored on the medium, the user re-mounts the medium on the personal computer. In this state, when the user initiates a dedicated utility, environment setting for wireless communication based on the variety of items of information stored on the medium is performed and a connection request with the random numbers added thereto is transmitted to the projector. The projector received this connection request replies a permission notification on condition of coincidence in random numbers and the personal computer received this notification automatically starts to transfer the display data.